Phytic acid. A natural antioxidant

The catalysis by iron of radical formation and subsequent oxidative damage has been well documented. Although many iron-chelating agents potentiate reactive oxygen formation and lipid peroxidation, phytic acid (abundant in edible legumes, cereals, and seeds) forms an iron chelate which greatly accelerates Fe2+-mediated oxygen reduction yet blocks iron-driven hydroxyl radical generation and suppresses lipid peroxidation. Furthermore, high concentrations of phytic acid prevent browning and putrefaction of various fruits and vegetables by inhibiting polyphenol oxidase. These observations indicate an important antioxidant function for phytate in seeds during dormancy and suggest that phytate may be a substitute for presently employed preservatives, many of which pose potential health hazards.     

Antioxidant potential of ferulic acid.

Ferulic acid is a ubiquitous plant constituent that arises from the metabolism of phenylalanine and tyrosine. It occurs primarily in seeds and leaves both in its free form and covalently linked to lignin and other biopolymers. Due to its phenolic nucleus and an extended side chain conjugation, it readily forms a resonance stabilized phenoxy radical which accounts for its potent antioxidant potential. UV absorption by ferulic acid catalyzes stable phenoxy radical formation and thereby potentiates its ability to terminate free radical chain reactions. By virtue of effectively scavenging deleterious radicals and suppressing radiation-induced oxidative reactions, ferulic acid may serve an important antioxidant function in preserving physiological integrity of cells exposed to both air and impinging UV radiation. Similar photoprotection is afforded to skin by ferulic acid dissolved in cosmetic lotions. Its addition to foods inhibits lipid peroxidation and subsequent oxidative spoilage. By the same mechanism ferulic acid may protect against various inflammatory diseases. A number of other industrial applications are based on the antioxidant potential of ferulic acid.     

Impact of Phytic Acid on the Physical and Oxidative Stability of Protein-Stabilized Oil-in-Water Emulsions

The effects of phytic acid on the physical and oxidative stability of flaxseed oil-in-water emulsions containing whey protein-coated lipid droplets were investigated. The surface potential, particle size, microstructure, appearance, and oxidation of these emulsions were monitored when they were stored at pH 3.5 and 7.0 for 25 days in the dark (37 °C). The phytic acid and protein-coated lipid droplets had similar charges (both negative) at pH 7.0, but had opposite charges (negative and positive) at pH 3.5. At pH 7.0, the addition of phytic acid had no impact on the physical stability of the emulsions but significantly improved their oxidative stability, which was attributed to its ability to sequester pro-oxidant transition metals (iron ions). At pH 3.5, extensive droplet aggregation and creaming occurred in the emulsions containing phytic acid, which was ascribed to charge neutralization and ion bridging. The oxidative stability of the acidified emulsions, however, still increased after addition of phytic acid, which was again attributed to its ability to chelate iron ions. Interestingly, the antioxidant activity of phytic acid decreased as its level was increased. Our results suggest that phytic acid may be used as a natural antioxidant to improve the oxidative stability of food emulsions containing polyunsaturated fatty acids, but its level must be carefully controlled.

     

玉米中植酸代谢研究的策略

作物尤其是玉米的种子中积累了丰富的植酸。早先的研究侧重于降低种子中植酸的含量,但是随着人们对植酸认识的深入,发现植酸对于动、植物而言具有不可替代的生物功能。对于人和动物而言,植酸有抗营养作用,但也是重要的健康因子;对于植物而言,植酸及其代谢中间体的生物学功能却缺乏明确的研究。若要明确把握植酸的育种方向,就必须对植酸在植物中的合成过程有明确的认识。但自植酸被发现至今,人们对于其在高等植物中的合成过程仍然知之甚少,对其生物学功能更是缺乏全面的了解。本文综述了植酸代谢研究的现状,分析并总结了植酸的代谢通路,指出了植酸代谢研究的突破点,结合植酸代谢的研究特点和进展,比较了基因同源克隆、关联分析等4种最具潜力的研究策略。     

Origin and seed phenotype of maize low phytic acid 1-1 and low phytic acid 2-1

Phytic acid (myo-inositol-1, 2, 3, 4, 5, 6-hexakisphosphate or Ins P(6)) typically represents approximately 75% to 80% of maize (Zea mays) seed total P. Here we describe the origin, inheritance, and seed phenotype of two non-lethal maize low phytic acid mutants, lpa1-1 and lpa2-1. The loci map to two sites on chromosome 1S. Seed phytic acid P is reduced in these mutants by 50% to 66% but seed total P is unaltered. The decrease in phytic acid P in mature lpa1-1 seeds is accompanied by a corresponding increase in inorganic phosphate (P(i)). In mature lpa2-1 seed it is accompanied by increases in P(i) and at least three other myo-inositol (Ins) phosphates (and/or their respective enantiomers): D-Ins(1,2,4,5,6) P(5); D-Ins (1,4,5,6) P(4); and D-Ins(1,2,6) P(3). In both cases the sum of seed P(i) and Ins phosphates (including phytic acid) is constant and similar to that observed in normal seeds. In both mutants P chemistry appears to be perturbed throughout seed development. Homozygosity for either mutant results in a seed dry weight loss, ranging from 4% to 23%. These results indicate that phytic acid metabolism during seed development is not solely responsible for P homeostasis and indicate that the phytic acid concentration typical of a normal maize seed is not essential to seed function.     

Reduced phytic Acid content does not have an adverse effect on germination of soybean seeds

Altering the level of phytic acid phosphorus by nutritional means had no effect on the ability of soybean (Glycine max L. [Merr.], cv `Williams 79') seeds to germinate under laboratory or greenhouse conditions. Dry matter moved out of the cotyledons at similar rates whether the germinating seeds initially contained low (0.19), medium (0.59), or high (1.00 milligram per seed) phytic acid phosphorus. Growth of roots and shoots from 3 to 9 days after planting was similar for seeds containing low and medium levels of phytic acid phosphorus. The medium level of phytic acid resembles that found in field-grown seed, so it is clear that soybean seeds normally contain a phosphorus reserve far above that needed for germination and early seedling growth.     

Phytic acid and raffinose series oligosaccharides metabolism in developing chickpea seeds

Phytic acid and raffinose series oligosaccharides (RFOs) have anti-nutritional properties where phytic acid chelates minerals and reduces their bioavailability to humans and other animals, and RFOs cause flatulence. Both phytic acid and RFOs cannot be digested by monogastric animals and are released as pollutant-wastes. Efforts are being made to reduce the contents of these factors without affecting the viability of seeds. This will require a thorough understanding of their metabolism in different crops. Biosynthetic pathways of both metabolites though are interlinked but not well described. This study was made on metabolism of these two contents in developing chickpea (Cicer arietinum L cv GL 769) seeds. In this study, deposition of RFOs was found to occur before deposition of phytic acid. A decline in inorganic phosphorus and increase in phospholipid phosphorus and phytic acid was observed in seeds during development. Acid phosphatase was the major phosphatase in seed as well as podwall and its activity was highest at early stage of development, thereafter it decreased. Partitioning of ¹⁴ C label from ¹⁴ C-glucose and ¹⁴ C-sucrose into RFOs and phytic acid was studied in seeds in presence of inositol, galactose and iositol and galactose, which favored the view that galactinol synthase is not the key enzyme in RFOs synthesis.     

植酸对红豆杉细胞悬浮培养影响作用的研究

针对红豆杉细胞培养中经常遇到的褐变问题,以植酸做抗氧化剂,添加到悬浮细胞培养基中,能提高细胞鲜重,明显抑制细胞多酚氧化酶和过氧化物酶活性,从而有效地控制细胞褐变,促进红豆杉悬浮细胞生长。以005%浓度的添加效果最好。     

植酸切花保鲜剂的研究

本文报道以植酸作保鲜剂,对切花保鲜作用机理的研究。实验结果表明,植酸作为保鲜剂具抗氧化和抑制多酚氧化酶作用,从而显著延长切花保鲜期,为深层次开发利用植酸资源提供了重要依据。     

The maize low-phytic acid 3 encodes a myo-inositol kinase that plays a role in phytic acid biosynthesis in developing seeds

Phytic acid, myo-inositol-1,2,3,4,5,6-hexakisphosphate or Ins P6, is the most abundant myo-inositol phosphate in plant cells, but its biosynthesis is poorly understood. Also uncertain is the role of myo-inositol as a precursor of phytic acid biosynthesis. We identified a low-phytic acid mutant, lpa3, in maize. The Mu-insertion mutant has a phenotype of reduced phytic acid, increased myo-inositol and lacks significant amounts of myo-inositol phosphate intermediates in seeds. The gene responsible for the mutation encodes a myo-inositol kinase (MIK). Maize MIK protein contains conserved amino acid residues found in pfkB carbohydrate kinases. The maize lpa3 gene is expressed in developing embryos, where phytic acid is actively synthesized and accumulates to a large amount. Characterization of the lpa3 mutant provides direct evidence for the role of myo-inositol and MIK in phytic acid biosynthesis in developing seeds. Recombinant maize MIK phosphorylates myo-inositol to produce multiple myo-inositol monophosphates, Ins1/3P, Ins4/6P and possibly Ins5P. The characteristics of the lpa3 mutant and MIK suggest that MIK is not a salvage enzyme for myo-inositol recycling and that there are multiple phosphorylation routes to phytic acid in developing seeds. Analysis of the lpa2/lpa3 double mutant implies interactions between the phosphorylation routes.     

植酸对杂交水稻V20B种子萌发及生理特性的影响

以杂交水稻V20B 为材料,研究外源植酸对种子萌发的影响。结果表明,外源植酸浓度为10 mmol/L 时能明显抑制种子萌发。生理生化检测表明,植酸对杂交水稻种子萌发过程中α-淀粉酶活性、可溶性糖和内源植酸含量变化有不同程度的影响。     

The oxidation of endogenous ascorbic acid during histamine secretion by rat peritoneal mast cells

Endogenous ascorbic acid is oxidized to the free radical species by rat mast cells during histamine secretion. This antioxidant may function as a radical scavenger of Superoxide and other membrane-damaging radicals known to be liberated by this process. The high levels of ascorbic acid in mast cells may, therefore, function to protect the cell membrane from oxidative damage and thereby promote cell survival after an extensive secretory response.     

Effects of phytic acid on the myoglobin-t-butylhydroperoxide-catalysed oxidation of uric acid and peroxidation of erythrocyte membrane lipids

Phytic acid stimulated the myoglobin-t-butylhydroperoxide (TBHP)-catalysed oxidation of uric acid, but inhibited the peroxidation of erythrocyte membrane lipids induced by the same system. Butylated hydroxy-toluene, a free radical chain reaction-terminating antioxidant, also suppressed the myoglobin-TBHP-induced lipid peroxidation. Moreover, phytic acid inhibited the hydroxyl radical-induced degradation of deoxyribose, but the extent of inhibition in this system was reduced by increasing the ferric ion concentration, suggesting that these effects of phytic acid on the myoglobin-TBHP-mediated oxidation are more likely attributable to its metal chelating properties rather than to a free radical scavenging action. The effectiveness of phytic acid, a naturally occurring antioxidant, in the inhibition of both iron- (as previously shown) and myoglobin-dependent lipid peroxidation suggests its possible therapeutic application as a non-toxic antioxidant for ameliorating the extent of oxy-radical-mediated myocardial ischemia/reperfusion damage.Abbreviations ASC Ascorbic acid - BHT Butylated Hydroxytoluene - DMSO Dimethyl Sulfoxide - TBHP t-Butylhydroperoxide - TBA Thiobarbituric Acid - TBARS Thiobarbituric Acid-reactive Substances     

植酸在银杏组织培养中应用的研究

本文报道以植酸作抗氧化剂,对银杏愈伤组织抗氧化褐变的研究。结果表明:①植酸具有抑制多酚氧化酶活性的作用,从而有效地控制愈伤组织的褐变,促进愈伤组织生长;②不同的抗褐变剂,以0.1％的植酸效果最好;③不同的培养基以MT附加BA1.0 mg/L,NAA 3.0 mg/L的效果最好。     

The timing and rate of phytic Acid accumulation in developing soybean seeds

The time-course of phosphorus (P) accumulation in the phytic acid fraction of developing soybean (Glycine max [L.] Merr. cv `Williams 79') seeds as well as the relation of phytic acid P to total P content were determined. Phytic acid was detected early in embryogenesis in field-grown soybeans and accumulated in a linear fashion throughout most of seed development. Although the observed rates of accumulation ranged from 18.7 micrograms phytic acid P per seed per day in pods positioned low on the plant to 33.6 micrograms in pods positioned high on the plant, the final concentrations were the same in all cases. Nearly all of the P translocated to developing seeds was incorporated into phytic acid from the third week after flowering until physiological maturity, with the sum of nonphytic acid P compounds remaining constant. Phytic acid accumulation was also linear throughout development when soybean plants were grown in solutions having nutrient P levels that ranged from severely limiting (2.0 milligrams P per liter) to excess (50 milligrams P per liter). However, there was a pronounced effect on rate of accumulation, which ranged from 7.2 micrograms phytic acid per seed per day with limiting nutrient P to 44.7 micrograms with excess P. The change in level of phytic acid accounted for most of the alteration in total seed P that was caused by altering the P status of the plants. These results support the view that phytic acid synthesis is involved in P homeostasis of the developing soybean seed.     

植物种子植酸研究进展

磷是植物生长发育所必需的大量营养元素。在种子发育过程中,植酸是磷的贮存库,对维持植物体内磷平衡有重要的作用。在种子萌发过程中,植酸酶分解植酸盐,释放磷、矿质营养和肌醇供幼苗生长。本文综述了近年来植物(作物)种子中植酸的生物合成途径、种子植酸含量的遗传、低植酸作物的育种等研究进展。首先,植酸生物合成途径中最初的反应底物为葡萄糖-6-磷酸,形成肌醇后,以肌醇为底物合成植酸共有两条路径:依赖脂类与不依赖脂类,目前,已分离鉴定若干植酸合成所需的关键酶及其编码基因,包括肌醇-3-磷酸合成酶、肌醇激酶、肌醇多磷酸盐激酶,以及参与植酸运输的ATP结合盒转运子。其次,利用作图群体及关联分析群体,分别在水稻(Oryza sativa L.)、白菜(Brassica rapa L.)、菜豆(Phaseolus vulgaris L.)等植物中鉴定出多个与种子植酸磷含量相关的遗传位点。第三,筛选获得有价值的低植酸突变体是培育低植酸作物的主要途径。当把低植酸作为育种目标时,可能会忽略种子植酸含量的降低给植物带来的不利影响,如何消除低植酸造成的不利影响,成为科学家们亟需解决的问题。     

Approaches and challenges to engineering seed phytate and total phosphorus

About 75% of seed total phosphorus (P) is found in a single compound, phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate or InsP₆). Phytic acid is not efficiently utilized by monogastric animals (poultry, swine, fish), which creates phosphorus management and environmental impact problems in animal production. Phytic acid also functions as an antinutrient when consumed in human and animal diets. These problems can be addressed via feed or food supplementation with P and other minerals or phytase, or more efficiently and sustainably at their source by crop breeding or bioengineering of low-phytic acid/high-available P crops. However, since phytic acid and its synthetic pathways are central to a number of metabolic, developmental and signaling pathways important to plant function and productivity, low-phytate can translate into low-yield or stress susceptibility. The biological functions of phytic acid and identification of genetic resources and strategies useful in engineering high-yielding, stress-tolerant low-phytate germplasm will be reviewed here. One promising approach that can avoid undesirable outcomes due to impacts on phytic acid metabolism is to engineer “high-phytase” seeds. In contrast to the issue of seed phytic acid, there has been relatively little interest in seed total P as a trait of agricultural importance. However, seed total P is very important to the long-term goal of sustainable and environmentally friendly agricultural production. Certain low-phytate genotypes are also “low-total P”, which might represent the ideal seed P trait for nearly all end-uses, including uses in ruminant and non-ruminant feeds and in biofuels production. Future research directions will include screening for additional genetic resources such as seed total P mutants.